Urban Health Study (CAS 10067) The Urban Health Study is a human population-based, community-based, etiologic study of 2,400 San Francisco Bay area injection drug users who are exposed to a variety of blood borne viruses. The viruses of most interest cause hepatocellular carcinoma, non-Hodgkin lymphoma, cirrhosis and end-stage liver disease. This research has a molecular component: the specimens are being used to investigate gene markers that may be associated with disease. We make genetic comparisons between drug users who failed to become infected with HCV and otherwise similar HCV-infected subjects. We will also compare subjects who are chronically infected with HBV or HCV to those with resolved infection. HALT-C Study (CAS 10070) This study makes use of data and specimens that were collected from patients with chronic hepatitis C during the HALT-C trial, which evaluated the efficacy of long-term treatment with pegylated interferon plus ribavirin to prevent hepatocellular carcinoma and cirrhosis. We compare host genetic polymorphisms in HALT-C non-responders to HALT-C participants who responded to anti-viral treatment. This is a human population-based study in a clinical setting. This research has a molecular component in that DNA specimens are used to investigate gene markers that may be associated with treatment response. This study aims to detect genetic markers that make patients more likely to respond to anti-viral treatment and, therefore, less likely to develop hepatocellular carcinoma. HCC in the United States (CAS 10303) This study is human population-based and etiologic. The study setting is clinical and it includes patients with chronic HCV infection who are undergoing liver transplantation. This research has a molecular component in that specimens are being used to investigate genetic markers (liver gene expression) that may be associated with the development of hepatocellular carcinoma and cirrhosis. Human Immunodeficiency Virus Epidemiology Research Study (HERS) (CAS 10426) This research project is human population-based and etiologic The study setting is clinical and it is focused on infection with HIV, which causes non-Hodgkin lymphoma and Kaposi sarcoma. This research has a molecular component- specimens are being used to investigate gene markers that may be associated with HIV infection.